Proceedings Paper

Experiments done with single photons in the early 1990's produced a surprising result: that single photons pass through
a photonic tunnel barrier with a group velocity faster than the vacuum speed of light. This result has stimulated intense
discussions related to causality, the speed of information transfer, the nature of barrier tunneling and the meaning of
group velocity. The superluminality of tunneling photons is now textbook material, although the authors note that
controversy still remains. Another paradoxical result, known as the Hartman effect, is that the tunneling time of the
photons becomes independent of barrier length in the limit of opaque barriers. In this paper we examine the meaning of
group velocity in the context of barrier tunneling. We ask whether a single tunneling photon can be described by a
group velocity and whether the short group delays imply superluminal group velocity. We resolve the paradox of the
Hartman effect and show that the predicted and measured group delays are not transit times but photon lifetimes.